As you can see, my girls names are similar in style (feminine, 3+ syllable), but are very different when it comes to popularity, which makes it kind of tricky to figure out the 3rd name. What would you think works well with my children's names to complete my sibset for a boy and a girl? My husband is hoping for a boy, but I have a feeling we'll end up with a 3rd girl

You have a very sweet, rhyme like quality when you say your girls names. So sticking to that theme I like VictoriaMaeve. But if you don't want another "V" name, I would go for Elena. For a boy I would go strong and masculine - SamuelJohn is my pick